The present invention relates to a lance supporting apparatus for supporting a lance which is used in injecting a gas or a gas and a powdered treating agent (referred to as "powder", hereinunder) into a molten metal.
Japanese Patent Examined Publication Nos. 12246/1969, 21818/1971 and 22208/1970, as well as Japanese Patent Unexamined Publication No. 37112/1983, disclose methods for adjusting compositions of molten metals by injecting gases and/or powders into the molten metals which are under vacuum degassing process. The effect or efficiency of supply of the powder into molten metal is improved by increasing the chance of contact between the powder and the molten metal, i.e., the area and time of contact. The injecting of a gas and/or the powder strengthens the stirring of the molten metal without any risk of mixing with converter slag, thereby improving the purity and shortening the treating time.
The known system for injecting a gas and/or powder into molten steel employs an elongated lance which is mounted on a lance lift truck which is mounted at a predetermined inclination angle and is capable of moving up and down while rotating the lance. The distal end portion of the lance is immersed in the molten steel so as to be able to insert the gas and/or the powder into the molten steel. In order to maximize the effect of injecting the gas and/or the powder, it is necessary that the whole part of the gas and/or the powder is inserted into the molten steel without allowing them to escape outside the immersed portion of riser tubes in the vacuum degassing vessel, and also that the lance, which is subjected to heavy wear due to its task for strongly stirring hot molten steel, can be repaired or renewed safely and easily any time such a demand exists. Unfortunately, however, the conventional systems cannot satisfactorily meet these requirements, due to presence of various problems. Therefore, hitherto, it has been practically difficult to maximize the effect of addition of the gas and/or the powder.
More specifically, in the conventional system, the support for the vertical guide rails for guiding the movement of the lance is fixed to the column of the vacuum degassing vessel, so that the repair or renewal of the lance requires a suspension of operation of the vacuum degassing and manual labour under a severe condition in a restricted space. In addition, the operation of the lance has to be stopped even when there is no defect in the lance, whenever the refractories on the vacuum degassing vessel are repaired. Thus the rate of operation of the vacuum degassing vessel is decreased to cause a serious reduction in the yield, whenever the refractories of the vessel and/or the lance are repaired or renewed. On the other hand, the vessel or the lance has to be kept out of operation for a long time so that it is subjected to a drastic temperature change and, hence, experiences a heavy spalling, resulting in a shortened life of the refractories and, hence, a further reduction in the yield.
If the gas and/or powder inserted through the lance escapes outside the immersed portion of the riser tube in the vacuum degassing vessel, the treating time is impractically prolonged and the purification effect is reduced undesirably, while causing various problems or drawbacks such as the boiling of the molten steel surface, heavy wear of the vessel and heavy deposition of metals. For the purpose of shortening the treating time or enhancing the purifying effect, it is a common measure to increase the inserting rate of the gas and/or the powder and to increase the depth of insertion. This measure, however, tends to increase the escape of gas and the powder.
It is, therefore, highly desirable that the position of inserting of the gas is adjustable regardless of the operating condition, in order to avoid any escape of the gas and the powder. In the known system described hereinbefore, the adjustment of the inserting position is afforded only by rotation of the lance about its axis and the lift of the lance truck which is inclined at a predetermined angle and movable up and down along the guide rails. Thus, from the view point of eliminating the escape of the gas and the powder, the conventional system does not have any function for optimizing the inserting position in relation to variance in various factors such as the production and mounting precision of the lance, change in the inserting direction of the lance, rate of inserting of the gas and/or the powder, solid-to-gas ratio, flow of the molten steel, and so forth.